“Face Unlock” (as it’s known on Android) does work on some phones for apps like Monzo. According to ChatGPT, if a device has the right tech within it’s front camera setup (infrared camera of ToF sensor) then face unlock works with the biometric APIs for apps to use.
Apparently, Samsung Galaxy S10 and S20 series has them but not anything newer than that, which is surprising. All Pixels from the 4 upwards also has them.
So I can use my face to unlock the Monzo app on my Pixel 8 Pro.